In the present text, reference to the “axis” of a tire is a reference to its axis of revolution. Said axis defines an axial direction of the mold assuming that the tire is in the mold.
Fabricating a tire by vulcanizing a green tire blank is known. To this end, the blank is placed in a mold of the type comprising:                at least one axial member carrying at least one surface for molding a sidewall of a tire;        radial segments each carrying at least one surface for molding a tire tread; and        means for connecting the axial member with the radial segments, comprising first radial and axial locking surfaces carried by the axial member which can cooperate with second radial and axial locking surfaces, which are complementary to the first locking surfaces, carried by each radial segment, the first and second locking surfaces being displaceable relative to each other, between:                    an open position of the mold in which the complementary locking surfaces are separated; and            a closed position of the mold in which the complementary locking surfaces cooperate with each other.                        
A mold of said type comprises first and second axial members respectively carrying surfaces for molding the first and second tire sidewalls and is described, for example, in European patent EP-A1-0 436 495.
Normally, in order to vulcanize a green tire blank, said blank is placed in a mold of the above-mentioned type in the following manner.
Initially, the blank is placed in contact with the axial members, then each axial member is connected with the radial segments, in particular by axially displacing the first and second locking surfaces relative to each other between the open and closed positions of the mold.
Generally, in a conventional mold, the green blank is pressed against the molding surfaces of the axial members and radial segments of the mold using a pressurized flexible membrane cooperating with the inner surface of the blank. In the mold disclosed in EP-A1-0 436 495, the pressure of the membrane, which is necessary in order to mold a tire, also has the effect of stressing the complementary locking surfaces in their cooperation position, and thus keeping the mold closed. Since the molding pressure participates in locking the mold closed, the conventional mold is said to be self-locking.
However, in a mold of the above-mentioned type, the sidewall molding surfaces, carried by the first and second axial members, are integral with the first radial and axial locking surfaces, also carried by the first and second axial members. For this reason, axial displacement of the first and second locking surfaces relative to each other when closing and opening the mold causes relative displacement between the sidewall molding surfaces which are integral with the first locking surfaces and the surfaces for molding the tread carried by the radial segments. Said relative displacement causes the formation of an unwanted impression on each sidewall of the blank before it is vulcanized, by plastic deformation of said sidewall.